Use Q_UNUSED(updateRect) when building without QT_BUILD_INTERNAL

Change-Id: I3e5292bc09ae53bee5f8bb8c7c1922d1a20b2e10
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

tests/auto/widgets/graphicsview/qgraphicsview/tst_qgraphicsview.cpp

@@ -4075,6 +4075,8 @@ void tst_QGraphicsView::update()
         QTRY_COMPARE(view.lastUpdateRegions.at(0), QRegion(updateRect) & viewportRect);
     }
     QTRY_VERIFY(!viewPrivate->fullUpdatePending);
+#else
+    Q_UNUSED(updateRect);
 #endif
 }